tests: always make bundles, adapt build and tests

Make test bundles the default. Drop non-bundle build mode.
Also do all the optimizations and tidy-ups this allows, simpler builds,
less bundle exceptions, streamlined build mechanics.

Also rework the init/deinit macro magic for unit tests. The new method
allows using unique init/deinit function names, and calling them with
arguments. This is in turn makes it possible to reduce the use of global
variables.

Note this drop existing build options `-DCURL_TEST_BUNDLES=` from cmake
and `--enable-test-bundles` / `--disable-test-bundles` from autotools.

Also:
- rename test entry functions to have unique names: `test_<testname>`
  This removes the last exception that was handled in the generator.
- fix `make dist` to not miss test sources with test bundles enabled.
- sync and merge `tests/mk-bundle.pl` into `scripts/mk-unity.pl`.
- mk-unity.pl: add `--embed` option and use it when `CURL_CLANG_TIDY=ON`
  to ensure that `clang-tidy` does not miss external test C sources.
  (because `clang-tidy` ignores code that's #included.)
- tests/unit: drop no-op setup/stop functions.
- tests: reduce symbol scopes, global macros, other fixes and tidy-ups.
- tool1621: fix to run, also fix it to pass.
- sockfilt: fix Windows compiler warning in certain unity include order,
  by explicitly including `warnless.h`.

Follow-up to 6897aeb105 #17468

Closes #17590

configure.ac

@@ -651,29 +651,6 @@ AS_HELP_STRING([--disable-unity],[Disable unity (default)]),
 
 AM_CONDITIONAL([USE_UNITY], [test "$want_unity" = 'yes'])
 
-dnl -----------------------
-dnl whether to bundle tests
-dnl -----------------------
-
-want_test_bundles='no'
-AC_MSG_CHECKING([whether to build tests into single-binary bundles])
-AC_ARG_ENABLE(test-bundles,
-AS_HELP_STRING([--enable-test-bundles],[Enable test bundles])
-AS_HELP_STRING([--disable-test-bundles],[Disable test bundles (default)]),
-[ case "$enableval" in
-  yes)
-    want_test_bundles='yes'
-    AC_MSG_RESULT([yes])
-    ;;
-  *)
-    AC_MSG_RESULT([no])
-    ;;
-  esac ],
-    AC_MSG_RESULT([no])
-)
-
-AM_CONDITIONAL([USE_TEST_BUNDLES], [test "$want_test_bundles" = 'yes'])
-
 dnl ************************************************************
 dnl switch off particular protocols
 dnl